The present invention relates to a microwave amplifier for amplifying microwave power, and more particularly to a microwave amplifier for generating high output microwave power that is reduced in distortion for applications to satellite and cellular communication, and industrial, scientific, and medical technology.
The microwave amplifier has a field effect transistor such as a compound semiconductor field effect transistor which is superior in high speed and high frequency performances, for example, a GaAs field effect transistor. The microwave amplifier is required to have high output and high efficient performances or characteristics for realizing further reductions in size and power consumption thereof. For these purposes, it is required that the microwave amplifier is superior in linearity with a reduced relative modulation distortion to avoid any undesirable influence to other channels. If plural microwaves including different carrier frequencies are inputted into the single microwave amplifier, non-linearity of the microwave amplifier generates not only the relative modulation distortion also a secondary distortion due to differential frequency of the different carrier frequencies.
The microwave amplifier is so designed that plural field effect transistors are connected in parallel to each other to form a multiple finger structure and to increase a gate width. If the microwave amplifier is high in impedance in a low frequency band, then the increased secondary distortion appears on the frequencies of the input signals, whereby the input signals show mixing with the amplified signals at drain electrodes of the field effect transistors. As a result, the relative modulation distortion is increased. This means that the linearity of the field effect transistors is never utilized effectively.
In order to solve the above problem, it was proposed to have improved the distortion characteristic of the microwave amplifier even for amplifying the microwave including plural different carrier frequencies. This conventional technique is disclosed in Japanese laid-open patent publication No. 10-233638. FIG. 1 is a schematic diagram illustrative of a first conventional microwave amplifier having improved the distortion characteristic of the microwave amplifier for amplifying the microwave including plural different carrier frequencies, wherein plural field effect transistors are internally matched to each other for parallel operations thereof. The conventional microwave amplifier has an input gate electrode 70 for receiving inputs of plural input microwaves and an output drain electrode 76 from which a synthesized microwave is outputted. The conventional microwave amplifier has a distributor circuit 71, a first impedance-matching circuit 72, a second impedance matching circuit 82, a first field effect transistor circuit 73, a second field effect transistor circuit 83, a first bonding pattern 77, a second bonding pattern 87, a first micro-strip line 51, a second micro-strip line 52, a first capacitor 55, a second capacitor 56, a third impedance-matching circuit 74, a fourth impedance-matching circuit 84, and a synthesizer circuit 75. The distributor circuit 71 has a single input which is connected to the input gate 70 and a first output connected to the first impedance-matching circuit 72 and a second output connected to the second impedance matching circuit 82. The first impedance-matching circuit 72 has an input side connected to the first output of the distributor circuit 71 and an output side connected to an input side of the first field effect transistor circuit 73. The second impedance-matching circuit 82 has an input side connected to the second output of the distributor circuit 71 and an output side connected to an input side of the second field effect transistor circuit 83. The first field effect transistor circuit 73 has an input side connected to the first impedance-matching circuit 72 and an output side connected through the first bonding pattern 77 to an input side of the third impedance-matching circuit 74. The second field effect transistor circuit 83 has an input side connected to the second impedance-matching circuit 82 and an output side connected through the second bonding pattern 87 to an input side of the fourth impedance-matching circuit 84. The third impedance-matching circuit 74 has the input side connected through the first bonding pattern 77 to the first field effect transistor circuit 73 and an output side connected to a first input side of the synthesizer circuit 75. The fourth impedance-matching circuit 84 has the input side connected through the second bonding pattern 87 to the second field effect transistor circuit 83 and an output side connected to a second input side of the synthesizer circuit 75. The synthesizer circuit 75 has the first input side connected to the third impedance-matching circuit 74 and the second input side connected to the fourth impedance-matching circuit 84 as well as has an output side connected to the drain output electrode 76. Further, the first micro-strip line 51 and the first capacitor 55 are connected in series between the first bonding pattern 77 and a first ground electrode GND-1 to form a first LC circuit, wherein the first micro-strip line 51 is shorter than one-quarter microwave for smoothing the secondary distortion due to the differential frequency of the carrier frequencies. The second micro-strip line 52 and the second capacitor 56 are connected in series between the second bonding pattern 87 and a second ground electrode GND-2 to form a second LC circuit, wherein the second micro-strip line 52 is shorter than one-quarter microwave for smoothing the secondary distortion due to the differential frequency of the carrier frequencies.
The microwave signals including the plural different carrier frequencies are inputted into the input gate electrode 70 and the inputted microwave signals are then distributed by the distributor circuit 71 to both the first and second impedance-matching circuits 72 and 82 for executing the impedance-matching to the distributed microwave signals. The impedance-matched microwave signals are then amplified by the first and second field effect transistor circuits 73 and 83. The amplified microwave signals are further transmitted through the first and second bonding patterns 77 and 87 to the third and fourth impedance-matching circuits 74 and 84, wherein the secondary distortions of the amplified microwave signals due to the differential frequencies of the different carrier frequencies are smoothed by the first and second LC circuits having the first and second micro-strip lines 51 and 52 and the first and second capacitors 55 and 56. The amplified and smoothed microwave signals are then transmitted to the third and fourth impedance-matching circuits 74 and 84 for executing further impedance-matching to the signals. The impedance matched microwave signals are then transmitted to the synthesizer circuit 75 for generating a synthesized microwave output signal which is to be outputted from the drain output terminal 76.
If the microwaves including plural different carrier frequencies are inputted into the above conventional microwave amplifier, then the secondary distortion is generated due to the differential frequency of the carrier frequencies. If, for example, the microwave includes first and second carrier frequencies f1 and f2 different from each other, then the secondary distortion has a differential frequency defined to be |f2-f1| which increases the relative modulation distortion. For these reasons, the first and second LC circuits comprising the first and second micro-strip lines 51 and 52 and the first and second capacitors 55 and 56 are provided for reducing the impedance by the resonance. Further, the first and second LC circuits are connected to the first and second ground electrodes 55 and 56 respectively for smoothing and reducing the secondary distortion due to the differential frequency of the carrier frequencies.
The above described conventional microwave amplifier raises the following problems if the high output characteristics are required. In order to allow the microwave amplifier to have the high output characteristics, it is necessary to increase the gate width of the field effect transistors circuits included in the microwave amplifier, whereby the output power from the field effect transistors is increased. The increase in the output power from the field effect transistors, however, causes an increase in the secondary distortion due to the differential frequency of the carrier frequencies. The above conventional microwave amplifier has the first and second LC circuits which comprise the first and second micro-strip lines 51 and 52 and the first and second capacitors 55 and 56 for smoothing the secondary distortion. However, the first micro-strip line 51 is connected to an outside edge of the first bonding pattern 77, and also the second micro-strip line 52 is connected to an outside edge of the second bonding pattern 87.
In the above circumstances, it had been required to develop a novel microwave amplifier free from the above problem.
Accordingly, it is an object of the present invention to provide a novel microwave amplifier free from the above problems.
It is a further object of the present invention to provide a novel microwave amplifier capable of generating a distortion-reduced high output microwave power.
The present invention provides a microwave amplifier having: at least an amplifying device for amplifying a microwave including plural different frequencies, and the at least amplifying device having a first contact region extending in a width direction; and at least an output side impedance device being distanced from the at least amplifying device in a transmission direction perpendicular to the width direction, and the at least output side impedance device having a second contact region interconnected to the first contact region of the at least amplifying device, and the second contact region extending in the width direction, wherein at least a smoothing circuit connected to just or generally entire of the second contact region of the at least output side impedance device for smoothing a distortion generated by a differential frequency of plural different carrier frequencies included in a microwave signal to be amplified by the amplifying device.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.